1. Field of the Invention
The present invention relates generally to x-ray systems, devices, and related components. More particularly, exemplary embodiments of the invention concern structures configured to aid in the management of relative motion between two or more attached components.
2. Related Technology
The ability to consistently develop high quality radiographic images is an important element in the usefulness and effectiveness of x-ray devices as diagnostic tools. However, various factors or conditions relating to the construction and/or operation of the x-ray device may operate to materially compromise the quality of radiographic images generated by the device. Likewise, such conditions can impair the operation of therapeutic x-ray devices. These conditions include, among others, vibration caused by moving parts of the x-ray device, and various thermally induced effects such as the occurrence of physical changes in the x-ray device components as a result of high operating temperatures and/or thermal gradients. While conditions such as these are diverse, it is frequently the case that the conditions are related to each other in some way, often to the extent that the occurrence of one condition is a direct consequence of the occurrence of one or more other conditions.
By way of example, vibration may occur as a consequence of thermally-induced relative movement between components of the x-ray device. In particular, as the various components and mechanical joints are subjected to repeated elastic deformation under the influence of the extreme thermal cycles typically experienced in connection with the operation of an x-ray device, the connections between the components can loosen and the components may become misaligned or separated. Thus, during operation of the x-ray device, such misalignment and/or separation of components is often manifested in the form of vibration and/or noise.
Typically, the occurrence of such vibration is most prevalent where components are joined together through the use of fasteners or similar arrangements. On the other hand, vibration problems, while still cause for concern, may occur relatively less commonly where components have been permanently attached to each other, such as by welding or brazing for example.
Further, yet other factors sometimes exist that can also cause and/or aggravate vibration in the x-ray device. For example, relative differences in the thermal expansion rates of connected components may cause the components to separate from each other over a number of thermal cycles. As discussed below, the existence of vibration due to the foregoing, and other, conditions presents problems with respect to the quality of the radiographic images produced by the x-ray device, or with respect to the operation of therapeutic devices.
In general, the generation of a radiographic image involves the use of a cathode, or other electron emitter, to direct a beam of electrons at an anode, or target, having a target surface composed of a material such that, when the target surface is struck by the electrons emitted by the cathode, x-rays are produced. In order to produce a high quality image or achieve some other desired result, the electrons of the electron beam are focused at a particular location, or focal spot, on the surface of the target.
In general, the quality of the radiographic images produced by the x-ray device depends largely on reliable and consistent positioning of the focal spot. Thus, any changes to the location and positioning of the focal spot, such as may occur as a result of vibrations or other conditions, during the generation of the radiographic image can materially impair the quality of the generated image and, thus, the effectiveness of the x-ray device. Operation of therapeutic devices likewise relies on maintenance of the focal spot location.
While any number of x-ray device components and assemblies may be adversely affected by vibration, the anode assembly, sometimes also referred to as the target assembly, is particularly susceptible to vibration related problems. This is due at least in part to the fact that at least some of the various components of anode assemblies are attached together with fasteners, rather than by processes such as welding or brazing.
In light of the foregoing concerns, various approaches have been taken with a view towards reducing the vibration that occurs as a result of relative movement between attached components of the x-ray device. In one approach, an interference fit, implemented either by thermal interference or pressing, is employed between the attached components. However, both of these approaches to interference fitting have proven problematic.
With respect to the interference press fit for example, significant forces must be exerted on the constituent portions of the assembly in order to join those portions together. Moreover, the resulting fit between the components of an assembly is often unsatisfactory because the runout between the components is unacceptably large. The runout may be the result of the presence of burrs or other assembly related conditions. A related concern is that such problems often cannot be readily resolved. For example, an assembly must sometimes be disassembled and reassembled a number of times until a proper fit between the components of the assembly is achieved. However, where a total indicated runout (“TIR”) requirement for the assembly is relatively small, such as 0.001″ or less for example, it may not be possible to disassemble and reassemble the components and still maintain compliance with the TIR requirements.
Thermal interference fit processes are also problematic. For example, typical thermal fit processes employed in connection with the attachment of a pair of components to each other require that one of the components be heated and the other component be cooled so that the component that has contracted as a result of the cooling process can be readily positioned within the component that has expanded as a result of the heating process. Because the temperature differential between the components must often be quite large for the assembly process to be effective, the handling of very cold and/or very hot components can be hazardous to the assembler. Moreover, the assembly process must be performed relatively quickly because the large temperature differential between the components exists only for a short period of time.
In yet another alternative approach, one of the components of an assembly is configured so as to allow for a measure of compliance in the radial direction. Such components thus obviate the need for the thermal processes necessitated by thermal interference fits. These compliant components also eliminate the need for exertion of large forces such as are typically employed in non-thermal interference fit processes. However, while these types of compliant components eliminate some problems, those components introduce new problems.
For example, the introduction of radial compliance means that the compliant component necessarily lacks radial stiffness. The lack of radial stiffness can be problematic inasmuch as components constructed in this fashion may permit more relative movement of an attached component in the radial direction than is desirable. Such movement may have various undesirable effects, including lowering a critical resonance point associated with a rotating assembly and/or permitting unacceptable levels of anode assembly motion at relatively high g-force levels.
Yet another approach to the resolution of problems such as those noted above involves the use of parts configured such that an intentional radial clearance is defined between the parts. At least one concern with this approach is readily apparent. Particularly, the radial clearance between the parts permits movement of each part relative to the other.
Another concern with approaches involving the intentional introduction of radial clearances between joined parts relates to the respective thermal expansion coefficients of those parts. That is, exposure of the assembled parts to thermal gradients such as are commonly experienced in x-ray device operating environments can result in relative motion between the parts as one part expands more quickly than the other. In one particular example, the component with the relatively higher coefficient of thermal expansion may, during operation of the device in which the assembly is employed, contact a radial surface of the component with the relatively lower coefficient of thermal expansion. After this contact is made, the addition of more heat to the assembly may cause the faster expanding component to push off the radial surface of the more slowly expanding component, thus resulting in unwanted relative movement between the attached components.
In view of the foregoing, and other, problems in the art, it would be useful to provide structures configured to aid in the management of relative motion between two or more attached components.